(1) Field of the Invention
The present invention relates generally to video data transmission systems and more particularly to the control of communication networks and the measurement of video quality.
(2) Description of the Prior Art
An IBM Video System (IVS) includes a high-bandwidth, switched network connecting 6 cities in the continental United States that is used by broadcasters to transmit and receive broadcast video. The system converts a subscriber""s analog or digital video to compressed digital format, then routes it to the destination over an asynchronous transfer mode (ATM) switched connection where the digital video is decompressed, converted back into analog or digital video and passed on to the receiving end. The video signal is compressed using MPEG-2 encoding format at a bit rate of 8-40 Mbps using real-time encoding and, in many cases, it is played out directly to air.
Using ATM as a backbone enables IVS to offer point to multipoint capability that is of value to the broadcast video industry. A single broadcast feed originating in New York City may be simultaneously routed to Los Angeles, Chicago and Atlanta. The ATM network provides subscribers with a high level of security and protection of content.
Typically, a broadcaster reserves in advance IVS network bandwidth for a given time slot. Immediately prior to the requested time, a connection(s) is established through the ATM network and the circuit is turned over to the broadcaster. At the end of the purchased time slot, the circuit is automatically disconnected.
Subscribers gain access to the IVS network via gateways referred to as Points-Of-Presence (POPS). All command and control are accomplished from a remotely located Command and Control Operations Center (CAC). There is no local control at the pops which are unmanned by designed. The volume of traffic, the intricacies of controlling network resources and the speed at which connections must be established preclude manual control of the network by operators. Operator intervention is far too cumbersome to achieve the necessary circuit connect/disconnect times. Network operations must be fully automated to provide the level of service expected by subscribers and to operate the network economically.
Broadcast engineers are a demanding customer set with exacting standards for video quality and availability of service. Since the subscriber""s feed is broadcast directly to air via the IVS network, any degradation or interruption of video signal will be obvious to television viewers and may result in a significant loss of revenue to the broadcaster. In a communications network, the carrier is responsible for demonstrating that the circuit it is providing meets applicable engineering standards. The carrier is further responsible for isolating transmission anomalies so that the network can be eliminated as the possible source or cause of the perturbation.
Because the network points-of-presence are unmanned, circuit testing in the IVS network is problematic. Although the techniques of EIA/TIA 250 C in-service testing are well known to broadcasters and remote testing is commonplace within the communications industry, testing is always accomplished with an engineer at one of the two sites involved in the circuit under test. Other carriers do not perform remote testing of terrestrial point-to-multipoint digital video circuits. Video quality testing is required of each and every circuit in the network prior to release to the subscriber. These tests cannot have a duration longer than a few seconds and if a failure is encountered, another circuit must be established. All circuit reservations are guaranteed and connection provisioning must be completed prior to the reservation start time.
In addition to pre-service circuit testing, each circuit is periodically tested while the feed is active and once again prior to disconnection. This non-invasive monitoring of video and audio quality detects problems near-real time so that service may be restored with minimum outage. It is common practice in the broadcast industry to record the on-air feed and subscribers are able to provide evidence of circuit degradation. In-service testing indemnifies the network should a subscriber claim network culpability for any such circuit anomaly.
Operating in a network using real-time MPEG-2 compression and ATM routing can cause perturbations not normally seen in a non-compressed digital and even analog network. Such problems as video tiling or breakup, loss of video and audio synchronization, audio clipping, dropouts and video freeze frames require a wider range of tests to be run to ensure the network is not distorting the broadcast.
Quiesced hardware such as encoders, decoders, switch ports, etc. and idle ATM trunks, referred to hereafter as network resources, must be regularly tested to ensure availability. Future reservations are guaranteed based on this availability and when hardware failures are detected, the network resource database must be updated to reflect the loss of such components. Loss of resources that affect reservations in the near term requires network management software to recalculate the resource allocation necessary to honor those reservations. Lastly, as maintenance actions at the POPs are completed, diagnostic testing must be executed to verify the fix and update the network resource database to reflect the change in status.
For quality assurance and to minimize outages on high priority video circuits, video feeds must continuously be monitored by operations personnel in a round-robin fashion. This monitoring must be accomplished without manual intervention and must provide an accurate indication of what the subscriber is actually seeing.
Prior art related to remote out-of-service and in-service testing of a video transmission system without human intervention includes the following:
U.S. Pat. No. 5,506,832 (Arshi et al.) issued Apr. 9, 1996, discloses a method of testing a computer-based client/server conferencing system. A digitized video and voice data signal is sent from a server to a client that essentially checks the connectivity of the circuit. No test is performed for quality and user intervention is required to start the test.
U.S. Pat. No. 5,274,446 (Ashida) issued Dec. 28, 1993, discloses an internal self-diagnosis of an image transmission device that processes digital video. Circuit loop backs are employed throughout the device for isolating failures to a component. The diagnostic capability is limited to the device itself. No test signals are sent to the remote end which precludes testing of the transmission network. User intervention is required to initiate the self test.
U.S. Pat. No. 5,446,492/U.S. Pat. No. 5,596,364 issued Aug. 29, 1995, and Jan. 21, 1997 respectively, disclose a system and method for measuring the video quality of transmission channels. The quality is measured by the audio delay, the video delay and perceptual degradation in video quality using extracted signals from the source and destination audio-visual signals in the transmission channel which does not include a switched digital ATM network. These signals are easily and quickly communicated between source and destination locations.
Accordingly, a need exists for in-service and out-of-service testing without human intervention in high bandwidth, switched network video transmission systems.
An object of the invention is a set of software executives that automate testing of a compressed digital video network precluding the need for -manual intervention.
Another object is a set of software test executives which update the network resource and reservation databases as components of the network malfunction or undergo repair action.
Another object is a set of software test executives which automatically perform periodic in-service testing of active video feeds in a non-invasive, non-service affecting manner.
Another object is a set of software test executives which will automatically, and without operator intervention, reconfigure circuits to restore service to video feeds that fail in-service testing.
Another object is a set of software test executives which perform problem isolation to a failing system component when a test failure occurs.
Another object is a set of software test executives which periodically route video feeds into a Command And Control (CAC) center for real-time monitoring of video and waveform quality.
These and other objects, features and advantages are accomplished in a switched, digital high-broadband network which provides automated control and testing of analog video signals, encoded and decoded real time, into MPEG 2 digitized format with a high level of security and protection of content and without attendant degradation of the analog signal sometimes experienced in satellite transmissions. The switch network, typically an asynchronous transfer mode (ATM) network, has multiple gateways for connection to video signal sources and sinks. Each gateway includes an analog/digital video switch for receiving the video signals and distributing them to an MPEG 2 encoder for conversion into digital packets. A multiplexer is coupled to the encoder and a digital switch for inserting the multiplexed signal into the switched ATM network. The multiplexer and the digital switch encode destination address information into the digital packets to ensure proper routing. Each gateway further includes a de-multiplexer and MPEG 2 decoder connected to the digital switch for separating the digital packets from the ATM network into separate MPEG 2 streams subsequently decoded into analog video and returned to the video sinks. A command and control center is coupled to each gateway for remote testing of point-to-point and point-to-multipoint circuits; testing a switch circuit before and after the establishment of a connection to a customer; in service testing of MPEG 2 encoding content; detecting and isolating digital network problems, and off-line network testing and automating network utilization. The command and control center includes test executives which ensure the quality and availability of video traffic. The test executives run continuously run in parallel with network operations and reservation management software. The test executives both query and update the network resource and reservation databases. Testing is divided into two categories, in-service (IS) and out-of-service (OOS) testing. Although detailed test data are made available, operator consoles and logs provide pass/fail indications for ease of operability. To facilitate field maintenance actions and in-depth troubleshooting, the executives allow operators to take manual control of testing. A video feed monitor (VFM) routes all video feeds to a studio monitor and a waveform monitor/vectorscope in the CAC for quality assurance purposes. Each feed is viewed for 15 seconds at a time in serial fashion with the feed name displayed in graphics for identification. In this manner, a bank of 4 video and 4 waveform monitor/vectorscopes can assure 16 video feeds per minute.